1. Field of the Invention
The invention relates generally to rotary drilling systems, and more specifically to improvements for drilling systems as used in drilling and boring for roof bolting operations for tunnel construction, mining and the like.
2. Description of the Prior Art
In the fields of industrial, mining and construction tools, polycrystalline diamond (PCD) is now in wide use in making cutting tool inserts, sometimes called polycrystalline diamond compacts (PDC). PCD materials are formed of fine diamond powder sintered by intercrystalline bonding under high temperature/high pressure diamond synthesis technology into predetermined layers or shapes; and such PCD layers are usually permanently bonded to a substrate of xe2x80x9cprecementedxe2x80x9d tungsten carbide to form such PDC insert or compact. The term xe2x80x9chigh density ceramicxe2x80x9d (HDC) is sometimes used to refer to a mining tool having a PCD insert. xe2x80x9cChemical vapor depositionxe2x80x9d (CVD) and xe2x80x9cThermally Stable Productxe2x80x9d (TSP) diamond-forms may be used for denser inserts and other super abrasive hard surfacing and layering materials, such as layered xe2x80x9cnitridexe2x80x9d compositions of titanium (TiN) and carbon (C2N2)and all such xe2x80x9chard surfacexe2x80x9d materials well as titanium carbide and other more conventional bit materials are applicable to the present invention.
The principal types of drill bits used in rotary drilling operations are roller bits and drag bits. In roller bits, rolled cones are secured in sequences on the bit to form cutting teeth to crush and break up rock and earth material by compressive and percussive forces as the bit is rotated at the bottom of the bore hole as in mining operations. In drag bits, PCD or like cutting elements on the bit act to cut or shear the earth material. The action of some flushing fluid medium, such as fluid drilling mud, water or a compressed air/vacuum system, is important in all types of drilling operations to cool the cutting elements and to flush or transport cuttings away from the cutting site. It is important to remove cuttings from the hole to prevent accumulations that may plug water passages and otherwise interfere with the crushing or cutting action of the bit; and the cooling action is particularly important in the use of PCD/CVD/TSP cutters to prevent carbon transformation of the diamond material.
Roof drill bits are one form of a rotary drag bit used in roof bolting operations, which are overhead so the drilling operation is upward through earth structures of extremely hard rock or mineral (coal) deposits; and stratas of shale, loose (fractured) rock and mud layers are frequently encountered.
My prior U.S. Pat. Nos. 5,180,022; 5,303,787 and 5,383,526 disclose substantial improvements in HCD roof drill bits using PCD cutting elements constructed in a non-coring arrangement, and also teach novel drilling methods that greatly accelerate the speed of drilling action and substantially reduce bit breakage and change-over downtime.
My prior U.S. Pat. No. 5,875,858 discloses a compressor and air-water mixing system that greatly reduces the amount of water required for effective hole flushing while substantially reducing the amount of respirable dust. My prior U.S. Pat. No. 6,092,612 discloses rotary drilling systems including improvements in drive steel columns and secondary bore reamers whereby to ensure delivery of flushing fluid and effective bit and reamer cooling without substantial pressure loss, and especially using the low volume air mist system of my earlier work. My co-pending application Ser. No. 09/260,159 involved improvements in chuck adaptors for the connection of the drive steel to the chuck of a drilling machine, and my co-pending application Ser. No. 09/543,933 discloses heat management techniques for strengthening PCD and like hard surfaced disc compacts.
One continuing problem in the mining industry has been the high volume of noise generated by the drill bit and drive steel during drilling operations. Environmental regulations prescribe that the noise level shall not exceed 80 DB (maximum) during a work shift of 8 hours whereas the usual amount of noise generated is frequently at or in excess of 100 DB thereby requiring shorter work shifts. Another continuing concern is in the adaptation and utilization of new technology to provide improved drilling systems, apparatus and components.
The invention is embodied in improvements in rotary drilling systems for drilling bores in earth formations using a hard surfaced rotary drill bit, comprising a noise suppression system associated with a drive steel column for significantly reducing the audible decibel level of drilling generated noise, and dual bore-cutting elements for providing first and second bore cutting to the design bore-gauge specification therefor.
It is an object of the present invention to provide a rotary drilling system that provides a drive steel coupling arrangement for steel column members and a drill bit and having noise suppression means. Another object is to provide a drive steel column having dual bore drilling elements for starting a pilot bore and completing the bore to design specifications. Still other objectives of the invention include substantial noise and vibration abatement at the bore hole and in the drive steel and improved tandem bore-cutting features increasing penetration speed with lower noise generation. Another major objective is to provide a safe, strong drill steel that is dampened against vibration, operates at a significantly lower decibel level, drills at a straighter and faster penetration, and which is economically and correctly fabricated. These and other objects and advantages will become more apparent hereinafter.